Method and apparatus for heat treating agglomerates

ABSTRACT

A method and apparatus for heat treating agglomerates is disclosed. The larger particles are separated from the fines, and the larger particles are then discharged to a preheater where they are heated to a temperature above the desired heat treating temperature. The thus heated larger particles are then combined with the separated fines in such a manner to effect heating of the fines by the larger particles such that the temperature of the mixture is reduced to below the desired heat treating temperature. The heated mixture of the larger particles and fines is then heated at the desired heat treating temperature.

nlted States Patent [191 1 3,732,064

Jaquay 1 May 8, 1973 54 METHOD AND APPARATUS FOR HEAT TREATING AGGLOMERATES Primary Examiner.lohn J. Camby [75] Inventor: Louis H. Jaquay, Carnegie, Pa. Attorney-Pamela Utzler & welsh [7 3] Assignee: Dravco Corporation, Pittsburgh, Pa. [57] ABSTRACT Filedi g- 10, 1971 I A method and apparatus for heat treating ag- Appl. No.1 170,590

[52] US. Cl ..432/l3,432/16,432/61,432/72 [51] Int. Cl ..F27b 7/02 [58] Field of Search ..263/32 R, 36, 53 R [56] References Cited UNITED STATES PATENTS 2,004,381 6/1935 Middelboe ..263/53 3,331,595 7/1967 Nelson et a1. ...263/32 R 2,590,090 3/1952 DeVaney ..263/32 R glomerates is disclosed. The larger particles are separated from the fines, and the larger particles are then discharged to a preheater where they are heated to a temperature above the desired heat treating temperature. The thus heated larger particles are then combined with the separated fines in such a manner to effect heating of the fines by the larger particles such that the temperature of the mixture is reduced to below the desired heat treating temperature. The heated mixture of the larger particles and fines is then heated at the desired heat treating temperature 12 Claims, 1 Drawing Figure METHOD AND APPARATUS FOR HEAT 7 TREATING AGGLOMERATES This invention relates to a method and apparatus for heat treating agglomerates containing particles of varying sizes, including fines.

In various processes for heat treating agglomerate masses, the agglomerates are fed into a vessel and heated by radiation or with heated gases flowing through the vessel. in some processes it is desirable to use heated gases in order to both heat the material and create the needed atmosphere for accomplishing certain chemical reactions within the vessel. One such process in the heat treating of copper oxide ore where a reducing atmosphere such as would be created by carbon monoxide is needed for reducing the ore to lower oxide or to the metallic state. In reducing copper oxide ore, the ore is fed into a rotary kiln where it is heat treated with heated carbon monoxide gases directed through the discharge end of the kiln to flow countercurrent to the flow of the ore. The ore is preheated at the entry end of the kiln and finally heat treated towards its discharge end. Large quantities of heated carbon monoxide flowing at high velocities are usually used in achieving the desired heat treatment. One problem with use of the high velocity heated gases is that the dust and fines in the ore mass tend to become entrained in the stream of gas to be carried out of the kiln and wasted.

Another problem in heat treating agglomerates in the manner in which copper oxide ore is treated, as noted above, is that the heat treating vessels are loaded to less than capacity so as to allow room for the flowing gases to pass through the vessel and intimately contact the material. In treating copper oxide ore with heated carbon monoxide, the kiln is filled at around ten percent of its volume. It is desireable to pass more ore through the kiln but if more were fed into the kiln, it would not be properly heat treated unless a prohibitively long kiln were used.

The above noted probiems with respect to heat treating agglomerate masses are overcome by virtue of the present invention whereby dust and fine entrainment is minimized while at the same time the throughput of the heat treating vessel is significantly increased. More particularly, these results are achieved by providing a method and apparatus for treating agglomerates containing particles of varying sizes, including fines, where the method preferably comprises the steps of: separating the larger particles from the fines; discharging the larger particles into a preheater; heating the larger particles in the preheater to a temperature above the desired heat treating temperature; combining the thus heated larger particles with the separated fines in such a manner to effect heating of the fines by the larger particles; and heating the mixture of the larger particles and fines at the desired heat treating temperature. The apparatus of the present invention preferably comprises in combination: separating means for separating the larger particles and fines forming an agglomerate mass; preheater means arranged to receive the larger particles from the separating means for heating the larger particles, the preheater including a separate burner; mixing chamber means for receiving the heated larger particles from the preheater means and the fines from the separating means and for intimately mixing the larger particles and fines in such a manner that the fines are heated; and heat treating vessel means disposed to receive the heated mixture of larger particles and fines from the mixing chamber and for heat treating the mass of material. Thus, by providing means for separating the larger particles and fines together with a preheater having a separate burner for heating the larger particles prior to final heat treating, and means for combining the heated larger particles and fines prior to final heat treating, the dust entrainment by the heating gases is significantly reduced because low velocity gases may be used in the heat treating vessel since the mass of material may be preheated to a temperature close to the final heat treating temperature and only low velocity heating gases would be needed for maintaining the heat treating temperature. Also, the exhaust gases from the heating vessel may be burned in the preheater since the preheater has a separate burner and thus, large quantities of heated gases would not be needed for preheating, such as would be the case where temperatures in the range of l200 F. to l500 F. would be required in the preheater. Additionally, increased amounts of material may be fed into the heat treating vessel, as compared with amounts previously used, due to the reduced quantity of heated gases required to maintain the heat treating temperature. Also, the desired time and temperature profile required for treating a mass of material can be achieved at high thermal efficiency since no preheating of the mass is required in the heat treating vessel. Finally, the present invention is simply constructed and may be practiced with reasonably low cost equipment.

The above noted advantages of the method and apparatus of the present invention are particularly applicable in systems for reducing non-ferrous ores such as copper oxide ores. In reducing such ores, carbon monoxide is used which may be burned by the burner of the preheater for heating the separated large particles. Also, the low velocity-low quantity carbon monoxide requirement needed for final heat treatment because of preheating the large particles to above the. final heat treating temperature would result in copper oxide ore reduction system which would be both efficient and less expensive to construct and operate as compared to currently used systems. It is to be noted, however, that these advantages are not limited to nonferrous ore reduction systems.

Other details and advantages of this invention will become apparent as the following description of a present preferred embodiment thereof and a preferred method of practicingv same proceeds.

in the accompanying drawings I have shown a present preferred embodiment of this invention and have illustrated a present preferred method of the same in which the single view shows in generally schematic representation heat treating apparatus embodying the present invention.

Referring now to the drawings, there is shown an apparatus, generally designated by the numeral 10, for treating agglomerates containing varying sized particles, such as copper oxide ore, for example, although not limited to such ore which is referred to herein simply for illustration purposes. The apparatus 10 illustrated includes a screening device 12 of any well known design for receiving unrefined ore for the purpose of separating the larger particles from the fines. The fines are discharged through a lower discharge conduit 14 to a conveyor such as screw conveyor 16 to be eventually reunited with the larger particles originally separated. The larger particles remain as the residue on the screening device 12 and are discharged onto a cross conveyor 18. The larger particles travel on cross conveyor 18 and are discharged on a conveyor 20 arranged on a rotating cover 22 forming the upper closure of an orbital preheater 24. The orbital preheater 24 is of a well known construction and per se is not part of the present invention. Such an orbital preheater 24 is fully disclosed in U. S. Pat. No. 3,403,895 issued to Paul E. Hatfield and Louis H. Jaquay and assigned to the assignee of the present application. The preheater 24 includes an outer bowl 25 and an annular hearth 26 with an opening 28 at the center thereof. The hearth 26 is sloped towards the opening 28 and is supported on suitable rollers for rotation about a generally vertical axis. An inner bowl 30 spaced from the sidewalls of outer bowl 25 serves to provide an annular material receiving space 32. Material is discharged from conveyor 20 through a hopper 34 which discharges through cover 22 into the space 32 between outer and inner bowls 25 and 30. Suitable seals 36 and 38, respectively, are provided between the cover 22 and the outer and inner bowls 25 and 30.

A mixing chamber 40 in the form of a duct or chute is arranged to communicate with the central opening 28 of hearth 26. Material heated on hearth 26 will discharge through opening 28 into chamber 40. Similarly, gases will pass from chamber 40 upwardly through opening 28, through the material on the hearth 26, thence through annular space 32 and finally through discharge openings 42 at the upper section of the sidewalls of outer bowl 25 and into manifold or bustle pipe 44. An exhaust fan 46 is connected to bustle pipe 44 for carrying away the waste exhaust gases.

Suitable seals 50 are provided for sealing the hearth 26 to the mixing chamber 40. Seals 50, as well as seals 36 and 38, may be water or sand seals which are wellknown in the art.

A burner 54 is provided and is arranged within the interior of the inner bowl 30 and extend through the bottom wall of the inner bowl for directing a flame in the vicinity of the central opening 28 of hearth 26. Burner 54 provides the ignition source for burning the gases entering the preheater through opening 28.

Mixing chamber 40 has a lower discharge opening coupled to the entry of an elongated rotary kiln 60 disposed at a slope to the horizontal. Rotary kiln 60 is of any well-known construction for use in heat treating material. The discharge end 62 of kiln 60 is coupled with a source of high temperature gas such as carbon monoxide for use in heat treating copper oxide ores. The discharge end of screw conveyor 16 is connected to a sidewall of mixing chamber 40 whereby the fines separated by screening device 12 will be discharged into the mixing chamber to be mixed with the heavier particles discharging from the hearth 26. The fines are arranged to be discharged by screw conveyor 16 into mixing chamber 40 at a generally upper position of the chamber whereby the fines will intimately mix with the heated heavy particles and consequently be heated thereby.

In a typical operation of the above described apparatus for heat treating copper oxide ore, crushed ore in an amount of about 5000 tons per day is fed onto screening device 12 where all fines sized less than 20 mesh pass through the screen into discharge conduit 14. The heavier ore particles are discharged onto cross conveyor 18 and then onto conveyor 20 and into preheater 24. The preheater 24 could be around ten feet high with an outer diameter of around thirty six feet and an inner diameter of around twenty nine feet, to provide a shaft area of about 400 square feet. The length of rotary kiln 60 could be around feet with an outside diameter of 13 feet. The slope of the kiln 60 with respect to a horizontal plane could be around 0.60 inch per foot, and could be rotated at around 1.5 R.P.M. In the apparatus described, the kiln 60 could be filled to as high as 25 percent capacity, as compared to around 10 percent in the prior art systems. An air and carbon monoxide mixture containing about five percent carbon monoxide, and heated to around 1800 F. is fed into the kiln 60 and will discharge at the feed end of the kiln at around 1200 F. The gases will flow through mixing chamber 40 and into preheater 24 through opening 21 of hearth 26. The burner 54 will burn the remainder of the unburned carbon monoxide in the gas stream with the resulting temperature of the entry gases onto the hearth 26 being around 2000 F. The heavier particles will be heated to around 950 F. at the point of discharge through opening 28. The exhaust gases leaving the preheater through bustle pipe 44 will be at around 350 F. The heavier particles leaving preheater 24 at around 950 F. will mix with the cold fines in mixing chamber 40 whereby the fines will be heated. The mixture of heavier particles and fines will reach an equilibrium temperature of around 900 F. and will enter the kiln 60 at that temperature. The 900 F. temperature of the mixture will be maintained through the kiln 60 and the mixture will discharge from the kiln 60 at that temperature. The mixture will be kept at 900? F. in the kiln 60 by passing the heated air and carbon monoxide entering the kiln at 1800 F. through the mixture at a rate of 200 SCFM of carbon monoxide and around 1700 SCFM of air. Similarly, the heavier particles entering the preheater at around 77 F. will be discharged at 950 F. with a gas flow of 2000 SCFM of carbon monoxide and 40,000 SCFM of air, with the gas entering the preheater at 2000 F.

By preheating the agglomerate mass prior to final heat treating in the kiln 60, the mass need only be maintained at the heat treating temperature within the kiln. Low velocity heating gases will accomplish the temperature maintenance, thereby reducing the problem of entrainment of fines by the gases. Since the heat treatment temperature in the kiln need only be maintained, a lower quantity of heated gas is necessary thereby permitting an increased amount of material to pass through the kiln. Thus, production rate for a given sized kiln will be increased compared with the prior art systems. Additionally, the thermal efficiency of the present invention is much improved over the prior systems since all of the carbon monoxide passing through the kiln is burned due to the fact that the preheater burns the exhaust gases discharging from the kiln. Thermal efficiency is also improved because the gases in the kiln are required to maintain the desired heat treating temperature rather than being required to heat the material in the kiln from a cold condition to the heat treatment temperature.

It should be noted that other type preheaters may be used as part of the present invention, rather than the orbital preheater disclosed so long as the preheater includes a separate burner. However, the orbital preheater has advantages of economy and efficiency over other preheaters such as another kiln or shell burners.

It is emphasized that the separate burner in the pre heater is an important feature in this invention. The burner allows the high preheat temperatures to be achieved without the need of large quantities of exhaust gases, being required for preheating such as in the case with the process and apparatus disclosed in U. S. Pat. No. 2,590,090 issued to F. D. DeVaney.

While I have shown and described a present preferred embodiment of this invention and have illustrated a certain present preferred method of practicing the same, it is to be distinctly understood that the invention is not limited thereto, but may be otherwise variously embodied and practiced within the scope of the following claims.

I claim:

1. The method of heat treating agglomerates containing particles of varying sizes, including fines, comprising the steps of:

screening the agglomerate mass to separate the larger particles from the fines;

discharging the larger particles into a preheater;

heating the larger particles in the preheater to atemperature above the desired heat treating temperature;

discharging the thus heated larger particles from the preheater;

combining the larger particles with the fines separated during the screening step, in such a manner to effect heating of the fines by the larger particles such that the temperature of the larger particles is reduced to below the desired heat treating temperature; and

heating the mixture of the larger particles and fines at the desired heat treating temperature.

2. The method as set forth in claim 1 wherein the second heating step uses heated gases flowing through the mixture; and wherein said gases are discharged into said preheater for use in the first heating step.

3. The method as set forth in claim 1 wherein the second heating step is performed while the mixture of larger particles and fines is moving.

4. The method for heat treating particulate matter containing agglomerates of varying sizes, including fines, comprising the steps of:

separating the larger particles from the fines;

discharging the larger particles into a preheater;

heating the larger particles in the preheater to a temperature above the desired heat treating temperature;

combining the thus heated larger particles with the separated fines; and

heating the mixture of the larger particles and fines at the desired heat treating temperature.

5. The method as set forth in claim 4 wherein said combining step is performed in such a manner as to effect heating of the fines b the larger particles.

6. The method as set orth in claim 5 wherein said combining step is performed in such a manner as to effect heating of the fines by the larger particles such that the temperature of the larger particles is reduced below the desired heat treating temperature.

7. The method as set forth in claim 4 wherein the secondheating step uses heated gases flowing through the mixture; and wherein said gases are discharged into said preheater for use in the first heating step.

8. Apparatus for heat treating agglomerates containing varying sized particles, including fines, comprising in combination:

separating means for separating the larger particles and fines forming the agglomerated mass;

preheater means arranged to receive the larger particles from said separating means for heating the larger particles, said preheater means including a separate burner;

mixing chamber means for receiving the heated larger particles from the preheater means and the fines from the separating means and for intimately mixing the larger particles and fines in such a manner that the fines are heated; and

gas heat treating vessel means disposed to receive the heated mixture of larger particles and fines from said mixing chamber means and for heat treating the mass of material.

9. The apparatus as set forth in claim 8 wherein said preheater means is an orbital preheater.

10. The apparatus as set forth in claim 8 wherein said heat treating vessel means includes an elongated rotary kiln.

1 1. The apparatus as set forth in claim 8 wherein said heat treating vessel means includes a source of heated gases arranged such that the gas will flow through the mixture of larger particles and fines; said heat treating vessel means has an exhaust for the heated gases; and wherein said mixing chamber means is arranged to receive the exhausted gases from said and direct the gases into said preheater means for burning by said burner and use in heating the larger particles.

12. In an apparatus for heat treating agglomerates including a separating means for separating the larger particles from the fines of the agglomerate mass, a preheater for receiving and heating the larger particles, mixing means for receiving the heated large particles and fines, and a gas heat treating vessel for receiving the mixture of particles from the mixing means and for heat treating the mass, the improvement therewith comprising burner means arranged within said preheater for burning the spent gases discharging from said heat treating vessel to provide the necessary heating medium for heating the larger particles in the preheater. 

1. The method of heat treating agglomerates containing particles of varying sizes, including fines, comprising the steps of: screening the agglomerate mass to separate the larger particles from the fines; discharging the larger particles into a preheater; heating the larger particles in the preheater to a temperature above the desired heat treating temperature; discharging the thus heated larger particles from the preheater; combining the larger particles with the fines separated during the screening step, in such a manner to effect heating of the fines by the larger particles such that the temperature of the larger particles is reduced to below the desired heat treating temperature; and heating the mixture of the larger particles and fines at the desired heat treating temperature.
 2. The method as set forth in claim 1 wherein the second heating step uses heated gases flowing through the mixture; and wherein said gases are discharged into said preheater for use in the first heating step.
 3. The method as set forth in claim 1 wherein the second heating step is performed while the mixture of larger particles and fines is moving.
 4. The method for heat treating particulate matter containing agglomerates of varying sizes, including fines, comprising the steps of: separating the larger particles from the fines; discharging the larger particles into a preheater; heating the larger particles in the preheater to a temperature above the desired heat treating temperature; combining the thus heated larger particles with the separated fines; and heating the mixture of the larger particles and fines at the desired heat treating temperature.
 5. The method as set forth in claim 4 wherein said combining step is performed in such a manner as to effect heating of the fines by the larger particles.
 6. The method as set forth in claim 5 wherein said combining step is performed in such a manner as to effect heating of the fines by the larger particles such that the temperature of the larger particles is reduced below the desired heat treating temperature.
 7. The method as set forth in claim 4 wherein the second heating step uses heated gases flowing through the mixture; and wherein said gases are discharged into said preheater for use in the first heating step.
 8. Apparatus for heat treating agglomerates containing varying sized particles, including fines, comprising in combination: separating means for separating the larger particles and fines forming the agglomerated mass; preheater means arranged to receive the larger particles from said separating means for heating the larger particles, said preheater means including a separate burner; mixing chamber means for receiving the heated larger particles from the preheater means and the fines from the separating means and for intimately mixing the larger particles and fines in such a manner that the fines are heated; and gas heat treating vessel means disposed to receive the heated mixture of larger particles and fines from said mixing chamber means and for heat treating the mass of material.
 9. The apparatus as set forth in claim 8 wherein said preheater means is an orbital preheater.
 10. The apparatus as set forth in claim 8 wherein said heat treating vessel means includes an elongated rotary kiln.
 11. The apparatus as set forth in claim 8 wherein said heat treating vessel means includes a source of heated gases arranged such that the gas will flow through the mixture of larger particles and fines; said heat treating vessel means has an exhaust for the heated gases; and wherein said mixing chamber means is arranged to receive the exhausted gases from said and direct the gases into said preheater means for burning by said burner and use in heating the larger particles.
 12. In an apparatus for heat treating agglomerates Including a separating means for separating the larger particles from the fines of the agglomerate mass, a preheater for receiving and heating the larger particles, mixing means for receiving the heated large particles and fines, and a gas heat treating vessel for receiving the mixture of particles from the mixing means and for heat treating the mass, the improvement therewith comprising burner means arranged within said preheater for burning the spent gases discharging from said heat treating vessel to provide the necessary heating medium for heating the larger particles in the preheater. 